Production method for fried foods

ABSTRACT

Disclosed herein is a method for producing fry, which comprises cooking with an oil composition containing at least 15% by weight of diglycerides as a frying oil, wherein the content of nitrogen in at least 5 liters of the oil composition is kept to 0.2% by weight or lower.  
     The method permits repeatedly producing fry good in appearance and flavor without causing coloring of an oil and emission of offensive odor in fry workshops, daily dish shops, eating houses, restaurants, etc. where fry is mass-produced over a long period of time using a diglyceride-containing oil composition having an effect to reduce the accumulation of body fat to prevent obesity.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a production method for friedfoods, which can prevent coloring of an oil or fat (hereafter referredto as “oil” merely) and emission of offensive odor when fry ismass-produced over a long period of time using an oil having a highcontent of diglycerides and give fry good in appearance and flavor.

[0003] 2. Description of the Background Art

[0004] It has been found that diglycerides have an effect to reduce theaccumulation of body fat to prevent obesity (Japanese Patent ApplicationLaid-Open Nos. 4-300826 and 10-176181). This is considered to beattributable to the fact that postprandial increase of neutral fat inblood is inhibited by ingestion of such diglycerides. It is also knownthat the use of diglycerides in frying has such merits that foaming uponpreparation of an oil is little, separation of the oil is good, andmouth feel becomes good (Japanese Patent Application Laid-Open Nos.7-16053, 10-127230, 11-243857 and 2001-61425, WO 00/77133, etc.). Fromsuch a point of view, oil compositions containing diglycerides in a highproportion have come to be widely used as household frying oil.

[0005] As described above, Since the diglycerides have an excellenthealthy function as described above, there is a particularly strongdemand for use of the diglycerides in fry workshops, daily dish shops,eating houses, restaurants, etc.

[0006] However, in institutional or processing oils used underparticularly severe conditions that fry is mass-produced over a longperiod of time, diglycerides may have been easily colored and emittedoffensive odor in some cases according to fry compared withtriglycerides. As a result, the appearance of the fry and workingenvironment have been impaired, and so the diglycerides have been unableto be applied to these uses. In addition, there has also been a problemthat the content of a diglyceride is lowered by heating over a longperiod of time, and so its excellent healthy function is deteriorated.

SUMMARY OF THE INVENTION

[0007] It is therefore an object of the present invention to provide aproduction method for fry, which can prevent coloring of adiglyceride-containing oil, lowering of content and purity ofdiglycerides and emission of offensive odor even under particularlysevere conditions that fried foods are mass-produced over a long periodof time and give fry good in appearance and flavor.

[0008] The present inventors have investigated the cause of coloring ofdiglyceride-containing oils. The diglycerides are almost never coloredin the household cooking time, namely, when about 30 minute-cooking offry is conducted 3 or 4 times in a quantity of oil of about 1 liter orless. However, it has been clarified that the diglycerides are rapidlycolored and emit offensive odor when it is used in institutional orprocessing oils for mass-producing fry over a long period of time. Sucha rapid change by particularly severe cooking is not observed on thetriglyceride which is a conventional oil, but is a phenomenoncharacteristic of the diglyceride. Thus, components indiglyceride-containing oil composition have been investigated. As aresult, it has been found that the coloring of the diglycerides is notdue to deterioration by heating or deterioration by oxidation that isobserved on the conventional oils, but is caused by nitrogen-containingcompounds dissolved out of materials of fry. It has also been found thatthe amount of the nitrogen-containing compounds dissolved can bedetermined by measuring a concentration of nitrogen in an oil. Thedissolution of the nitrogen-containing compounds is a specificphenomenon caused by the fact that the polarity of the diglycerides ishigher than the conventional oil (triglyceride). These findings have ledto finding of the present invention utilizing the diglycerides as afrying oil. It has also been found that when frying is conducted whilekeeping the nitrogen content to a specified value or lower, coloring andemission of offensive odor can be markedly prevented to mass-produce frygood in appearance and flavor.

[0009] According to the present invention, there is thus provided amethod of producing fry, which comprises cooking with an oil compositioncontaining at least 15% by weight of diglycerides as a frying oil,wherein the content of nitrogen in at least 5 liters of the oilcomposition is kept to 0.2% by weight or lower.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The method for the present invention comprises using an oilcomposition containing at least 15% by weight (hereafter indicatedmerely by “%”) of diglycerides. As described above, highdiglyceride-containing oils are used as household frying oils, but donot be used as institutional or processing oils under particularlysevere conditions that fry is mass-produced over a long period of time.It has heretofore been not known at all that such an oil composition israpidly colored and emits offensive odor under such conditions.

[0011] From the viewpoints of the physiological effect and industrialproductivity of the oil composition, the oil composition used in thepresent invention contains the diglycerides in a proportion of at least15%, preferably 30 to 100%, more preferably 50 to 100%, particularlypreferably 70 to 97%, most particularly preferably 80 to 95%. Otherglycerides than the diglycerides in the oil composition are amonoglyceride and a triglyceride, and the monoglyceride is preferablycontained in a proportion of at most 10% of the diglycerides.

[0012] It is preferred from the viewpoints of the physiological effectthat 55 to 100%, preferably 70 to 100%, more preferably 80 to 100,particularly preferably 90 to 100% of the constitutive fatty acids ofthe diglycerides be unsaturated fatty acids having 10 to 24 carbonatoms, preferably 16 to 22 carbon atoms. The residual constitutivesaturated fatty acids preferably have 14 to 24 carbon atoms, preferably16 to 22 carbon atoms. It is preferred from the viewpoints of theindustrial productivity that the constitutive fatty acids of themonoglyceride be the same as one of the constitutive fatty acids of thediglycerides. It is preferred from the viewpoints of the physiologicaleffect that 40 to 100%, preferably 55 to 100%, more preferably 70 to100, particularly preferably 80 to 100% of the constitutive fatty acidsof the triglyceride be unsaturated fatty acids having 10 to 24 carbonatoms, preferably 16 to 22 carbon atoms.

[0013] Since an oil composition that a proportion of a 1,3-diglyceridetherein is at least 15% inhibits increase of neutral fat in blood, whichforms the cause of adaults' diseases such as arteriosclerosis, reducesthe accumulation of body fat and is good in storage stability andflavor, it is desirable that an oil composition in which a proportion of1,3-diglyceride in the diglycerides is high, particularly, a proportionof the 1,3-diglyceride in the oil composition is at least 20%,preferably 40 to 100%, particularly preferably 45 to 95%, mostpreferably 50 to 90% also be used in the present invention.

[0014] It is desirable from the viewpoints of flavor and prevention ofsmoking that the content of the monoglyceride in the oil composition belower than 1.5%, preferably lower than 1.3%, more preferably 0.1 to 1%),and the acid value (AV, Standard oils and fats analyzing test method2.3.1-1996 (The Japan Oil Chemists' Society)) of the oil composition beat most 7, preferably at most 5, more preferably at most 3, particularlypreferably at most 2, most preferably at most 0.05 to 1. However, thecontent of the monoglyceride may be at most 8%, preferably 0.1 to 6%,more preferably 0.2 to 4%, and the acid value (AV) may be at most 20,preferably 0.1 to 10, more preferably 0.2 to 7, particularly preferably0.3 to 5 after use for frying.

[0015] Either a vegetable oil or an animal oil may be used as anoriginal of the oil composition used in the present invention. Specificexamples of such a raw material may include rapeseed oil, sunflower oil,corn oil, soybean oil, rice oil, safflower oil, cotton seed oil, linseedoil, palm oil, coconut oil, beef tallow, lard and fish oil. Fractionatedproducts thereof, and oils obtained by adjusting the melting pointsthereof by hydrogenation, transesterification or the like may also beutilized as raw materials.

[0016] The oil composition used in the present invention can be obtainedas a sole high diglyceride-containing oil obtained by an esterificationof a fatty acid derived from the above-described oil with glycerol or bymixing such an oil with the above-described raw oil. Excessivemonoglycerides formed by the reaction can be removed by thin filmdistillation or chromatography. These preparation processes are roughlydivided into chemical reactions may be carried out by a chemicalreaction making use of an alkali catalyst or the like. However, it ispreferred from the viewpoints of giving excellent flavor, and the likethat the reactions be carried out under enzymatically moderateconditions using a 1,3-position-selective lipase or the like.

[0017] The oil composition used in the present invention preferablyfurther comprises phytosterol. The phytosterol is a component having acholesterol-reducing effect. The content of the phytosterol in the oilcomposition used in the present invention is preferably at least 0.05%,particularly at least 0.3%. The content of phytosterol in a commonlysold oil composition prepared using, as a raw material, a fatty acidobtained by distillation is reduced. In such a case, the phytosterol maypreferably be added in such a manner that the content thereof amounts toat least 0.05%, and preferably falls within a range of 0.05 to 1.2%.When it is intended to reduce cholesterol to a greater extent thanordinary vegetable oils, the phytosterol may also be suitably added inan amount of 1.2 to 4.7%. Examples of the phytosterol used in thepresent invention include free substances such as α-sitosterol,β-sitosterol, stigmasterol, campesterol, α-sitostanol, β-sitostanol,stigmastanol, campestanol and cycloartenol, and besides esters thereof,such as fatty acid esters, ferulic acid esters and cinnamic acid esters.

[0018] To the oil composition used in the present invention, may befurther added a crystallization inhibitor.

[0019] Examples of crystallization inhibitors used in the presentinvention include polyol fatty acid esters such as polyglycerolcondensed ricinoleic acid esters, polyglycerol fatty acid esters,sucrose fatty acid esters, sorbitan fatty acid esters, polyoxyethylenesorbitan fatty acid esters and propylene glycol fatty acid esters.

[0020] Among these polyol fatty acid esters, polyglycerol fatty acidesters, sucrose fatty acid esters, sorbitan fatty acid esters whose HLB(Griffin's equation, J. Soc. Cosmet. Chem., 1, 311 (1949)) is at most 4,particularly at most 3 are preferred.

[0021] The crystallization inhibitor is preferably contained in aproportion of 0.02 to 0.5%, particularly preferably 0.05 to 0.2% in theoil composition used in the present invention from the viewpoint ofimproving stability at a low temperature.

[0022] To the oil composition used in the present invention, may befurther added an antioxidant, such as a natural antioxidant such astocopherol (VE), butylhydroxytoluene (BHT), butylhydroxyanisole (BHA),tert-butylhydroquinone (TBHQ), an ascorbic acid ester or rosemaryextract. These antioxidants are preferably contained in a proportion of50 to 5,000 ppm, particularly preferably 400 to 2,500 ppm in the oilcomposition. Further, an antifoaming agent such as a silicone may becontained in a proportion of 0.5 to 10 ppm, preferably 1 to 6 ppm.

[0023] An organic carboxylic acid may be further added to the oilcomposition used in the present invention. The organic carboxylic acidis an organic carboxylic acid, or a salt or derivative thereof. Exampleof the organic carboxylic acid include hydroxycarboxylic acids,dicarboxylic acids and tricarboxylic acids having 2 to 8 carbon atoms,preferably 2 to 6 carbon atoms. Specific examples thereof include citricacid, succinic acid and maleic acid, with citric acid being preferred.The total amount of the organic carboxylic acids is preferably 50 to2,000 ppm, more preferably 70 to 1,000 ppm, particularly preferably 100to 600 ppm, most preferably 150 to 300 ppm from the viewpoint ofoxidation stability and the effect of inhibiting hydrolysis.

[0024] In the method of the present invention, no particular limitationis imposed on the cooking time. However, the method is effective forcooking for at least 4 hours from the viewpoint of the prevention ofcoloring and emission of offensive odor. In particular, the presentinvention is useful in the case where the cooking is conducted for atleast 6 hours. The term “cooking time” as used herein means the timeduring which a frying oil is heated. Specifically, the cooking timeincludes the time during which frying is actually conducted, and thetime during which the oil is simply heated for preparation of materialsof fry or convenience' sake.

[0025] Since a diglyceride composition tends to be colored when a fryingtemperature is 140° C. or higher, it is desirable that the fryingtemperature be preferably at least 140° C., more preferably 150 to 200°C., particularly preferably 160 to 190° C., most preferably 170 to 190°C. No particular limitation is imposed on the frying time because itvaries according to the kind, form and size of materials of fry. Fromthe viewpoint of food sanitation, it is desirable to fry until thecenter temperature of a material of fry reaches 60° C. or higher,preferably 70 to 100° C., more preferably 75 to 100° C., particularlypreferably 80 to 100° C.

[0026] From the viewpoints of prevention of coloring and emission ofoffensive odor when the oil composition is used as an institutional orprocessing oil, the method of the present invention is particularlyuseful when frying is conducted under conditions that the total amountof the oil composition in a fryer is at least 5 liters, preferably 10 to100,000 liters, more preferably 18 to 10,000 liters, particularlypreferably 25 to 1,000 liters.

[0027] The feature of the method of the present invention resides inthat the content of nitrogen in the oil composition is kept to 0.2% byweight or lower, preferably 0 to 0.1%, more preferably 0 to 0.05%, stillmore preferably 0 to 0.01%, particularly preferably 0 to 0.005%, mostpreferably 0 to 0.003%. As shown in Examples which will be describedsubsequently, a diglyceride-containing oil composition is colored, theflavor of fry obtained is also deteriorated when the nitrogen content inthe oil composition exceeds 0.2%. In addition, offensive odor is emittedfrom the oil composition during heating, which is not preferable fromthe viewpoint of operating a fryer. Examples of means for keeping thenitrogen content to 0.2% by weight or lower include (a) a means in whichfrying is conducted while a new oil is added to replace a part of theold oil thereby, (b) a means in which a frying oil is treated with anitrogen adsorbent, (c) a means in which materials of fry, whosenitrogen content is 2% or lower, are used, and (d) a means in whichmigration of nitrogen from materials of fry, whose nitrogen contentexceeds 2%, into a frying oil is prevented. These methods may be usedeither singly or in any combination thereof.

[0028] In the means (a), the replacement of the oil is performed underconditions that the time required to replace the whole oil, which isdefined by the following equation (1), amounts 2 to 25 hours.

Time required to replace the whole oil (unit: hour)=(Total amount of oilin a fryer)/(Average amount of new oil supplied per hour)  (1)

[0029] More specifically, an oil in a fryer is absorbed in substances(materials of fry and coating) to be fried and gradually decreased. Theoil composition may be newly supplied by the decreased amount in such amanner that the whole oil in the fryer is replaced in 2 to 25 hours.Alternatively, a part of the oil in the fryer may be further taken outto newly supply the oil composition by an amount including the amounttaken out. If the time required to replace the whole oil exceeds 25hours, the nitrogen content exceeds 0.2% to show a tendency to becolored. If the time required to replace the whole oil is shorter than 2hours, the oil composition must be frequently replaced, which is notefficient from the viewpoints of cost and labor. The time required toreplace the whole oil is preferably 3 to 20 hours, more preferably 4 to17 hours, particularly preferably 5 to 15 hours. The diglyceridesdescribed in the present invention are converted into theircorresponding triglyceride and monoglyceride when they are heated for along period of time, and so their purities are gradually lowered. Inorder to prevent this fact, the oil replacing means (a) is effective. Atthis time, the time required to replace the oil is 2 to 25 hours likethe time required to inhibit coloring.

[0030] In the means (b) of treating with the nitrogen adsorbent, it isonly necessary to treat a frying oil with one of adsorbents such asactivated carbon, activated clay, silica magnesia, silica gel, silicaalumina, synthetic zeolite and ion-exchange resins, or a mixture orcomplex of 2 or more thereof. The concentration of the adsorbent to theoil is 0.01 to 5%, preferably 0.03 to 2%, more preferably 0.05 to 1.5%,particularly preferably 0.1 to 1%. If the concentration is lower than0.01%, the adsorption efficiency becomes poor. If the concentration ishigher than 5%, the amount of the adsorbent is too great forworkability. Specific examples thereof include a method in which theadsorbent is charged into a filter for removing the dregs of fry tofilter the frying oil, and a method in which the adsorbent is dispersedin the oil in a fryer and then separated by filtration using a filter orthe like.

[0031] In the means (c), examples of the materials of fry, whosenitrogen content is 2% or lower, include vegetables and cereals. Thenitrogen content in these materials of fry means a numerical valuebefore frying and must be 2% or lower from the viewpoints of preventionof coloring and emission of offensive odor. It is desirable that thecontent be preferably 0.1 to 1.8%, more preferably 0.2 to 1.6%,particularly preferably 0.3 to 1.4%. In this case, a coating is notessential. When a coating is used, the nitrogen content in the coatingis preferably 2% or lower, more preferably 0 to 1.8%, particularlypreferably 0.1 to 1.5%. Examples of fry corresponding to the materialsof fry in the means (c) include potato chips, fried potato, doughnut,snack confectionery, Japanese cracker (senbei), fried dough cookies(karinto), fried pie, fried cakes, fried bread and refrigeratedcroquettes.

[0032] In the means (d), examples of the materials of fry, whosenitrogen content exceeds 2%, include meat, fishes and shellfishes andeggs. In this case, it is necessary to prevent migration of nitrogenfrom the materials of fry into a frying oil. For example, the migrationof nitrogen can be prevented by wrapping materials of fry in an ediblefilm such as a coating of Chinese dumpling or rice paper like Chinesedumpling, shao-mai and harumaki or coating materials of fry with acoating of fry, tempura or fritter, starch, or the like. As with themeans (c), the nitrogen content in the materials of fry means anumerical value before frying, and it is preferably 2.1 to 10%, morepreferably 2.1 to 5%, particularly preferably 2.1 to 4%. Examples of frycorresponding to the materials of fry in the means (d) include friedmeat cakes, pork cutlets, fried fishes, fried prawns, friedcuttlefishes, fried oysters, chicken nuggets, food fried without coatand fried chickens.

[0033] It is preferred that at least 2 of the means (a) to (d) becombined with each other to keep the nitrogen content in the oilcomposition to 0.2% or lower. It is particularly preferred that thenitrogen content in the oil composition be kept to 0.08% or lower,preferably 0.05 or lower, particularly preferably 0.01% or lower, mostpreferably 0.005% or lower by a combination of (a), (b) and (c) or acombination of (a), (b) and (d).

[0034] In the method of the present invention, a proportion of the oilto the material of fry at the time of the beginning of frying ispreferably at least 1 part by weight, more preferably 2 to 50 parts byweight, particularly preferably 5 to 20 parts by weight per 100 parts byweight of the oil from the viewpoints of production efficiency andprevention of coloring and emission of offensive odor. When theproportion of the material of fry is lower than 2.5 parts by weight per100 parts by weight of the oil, the time required to replace the wholeoil is preferably 10 to 25 hours, particularly preferably 12 to 25hours. When the proportion is not lower than 2.5 parts by weight on theother hand, the time required to replace the whole oil is preferably 3to 20 hours, particularly preferably 5 to 20 hours.

[0035] Having generally described this invention, a furtherunderstanding can be obtained by reference to certain specific exampleswhich are provided herein for purpose of illustration only and are notintended to be limiting unless otherwise specified.

EXAMPLE 1

[0036] The following oil compositions were prepared.

[0037] Diglyceride Oil A:

[0038] Soybean oil fatty acid (650 parts by weight) and glycerol (107parts by weight) were subjected to esterification at 40° C. for 5 hoursunder 0.07 hPa using Lipozyme IM (product of Novo Nordisk Industry Co.).The enzyme was then separated by filtration, and the resultant filtratewas subjected to thin film distillation at 235° C. The distillate thusobtained was washed with water and then deodorized at 235° C. for 1 hourto obtain Diglyceride Oil A.

[0039] Diglyceride Oil B:

[0040] After a mixture of soybean oil fatty acid (455 parts by weight),the content of saturated fatty acids in which had been reduced bywinterization, rapeseed oil fatty acid (195 parts by weight) andglycerol (107 parts by weight) were subjected to esterification in thesame method as Diglyceride Oil A. The enzyme was then separated byfiltration, and the resultant filtrate was subjected to thin filmdistillation at 235° C. The distillate thus obtained was washed withwater and then deodorized at 235° C. for 1 hour to obtain DiglycerideOil B.

[0041] Diglyceride Oil C:

[0042] Hardened rapeseed oil fatty acid (IV=70, 650 parts by weight) andglycerol (107 parts by weight) were subjected to esterification at 40°C. for 5 hours under 0.07 hPa using Lipozyme IM (product of Novo NordiskIndustry Co.). The enzyme was then separated by filtration, and theresultant filtrate was subjected to thin film distillation at 235° C.The distillate thus obtained was washed with water and then deodorizedat 235° C. for 1 hour to obtain Diglyceride Oil C.

[0043] Invention Products 1 to 4 and Comparative Product 1:

[0044] Diglyceride Oil A, Diglyceride Oil B, Diglyceride Oil C andrapeseed oil (product of Hohnen Co., Ltd.) were mixed at theircorresponding weight ratios shown in Table 1. To the mixtures (each, 100parts) were added vitamin E (E Mix D, product of Eisai Co., Ltd.; 0.2parts by weight), silicone (KS-66, product of Shin-Etsu Chemical Co.,Ltd.; 0.0002 parts) and citric acid (0.02 parts) to produce InventionProducts 1 to 4 and Comparative Product 1. Analytic results of the oilcompositions thus obtained are shown in Table 1. TABLE 1 (weight ratio)Comp. Invention product product 1 2 3 4 1 Diglyceride Oil A 25 25 0 0 0Diglyceride Oil B 0 25 100 0 0 Diglyceride Oil C 0 0 0 100 0 Rapeseedoil 75 50 0 0 100 Composition of glycerides^(*1) TG 77.7 56.4 14.3 13.999.2 DG 22.0 42.9 84.6 85.1 0.7 MG 0.3 0.7 1.1 1.0 0.1 Composition ofconstitutive fatty acids^(*2) Triglyceride C16:0 5 5 3 4 5 C18:0 2 2 112 2 C18:1 60 58 38 77 62 C18:2 20 23 48 3 19 C18:3 8 8 8 1 8Diglyceride C16:0 12 7 3 4 n.t. C18:0 4 3 1 12 n.t. C18:1 24 31 38 77n.t. C18:2 51 50 48 3 n.t. C10:3 6 7 8 1 n.t. AV^(*3) 0.4 0.4 0.4 0.40.4

EXAMPLES 2 TO 4 Comparative Examples 1 to 3

[0045] (Repeated Test on Frying)

[0046] Each of the oil compositions (Invention Products 1 to 3 andComparative Product 1) prepared in Example 1 was used to repeatedly fryrefrigerated croquettes in accordance with Table 2 and the followingprocess. The nitrogen content in the oil composition in the course ofthe frying and the degree of coloring of the oil composition in thecourse of the frying and cooked products, odor in the vicinity of afryer upon cooking, and the diglyceride content in the oil compositionin the course of the frying were evaluated. The results are shown inTable 3.

[0047] (Material to be Fried, Frying Conditions)

[0048] Refrigerated croquettes: After potatoes (1.5 kg) were peeled, cutinto large pieces, washed with water and steamed to softness as it is.The steamed potato pieces were then smashed before being cooled, andcooled. Separately, minced pork (0.3 kg) and onion (0.3 kg) cut finewere frizzled with an oil in order and seasoned with common salt andpepper. Cabbage (0.1 kg) cut fine were added into this frizzled mixtureand frizzled. After putting out the fire, corn kernel (0.05 kg) wasadded, and the resultant mixture was sufficiently stirred. After thismixture was then sufficiently mixed with the smashed potato, theresultant mixture was divided into oval-shaped portions (about 50g/portion). Wheat flour, beaten egg and bread crumb were applied tothese portions. The croquettes thus obtained were refrigerated andstored (weight of croquette: about 75 g/croquette; weight ratio of thecoating: about 35%, nitrogen content in the coating: about 2.5%).

[0049] Amount of oil: 10 kg.

[0050] Fryer: Electric fryer (SEF-D9A type, manufactured by SanyoElectric Co., Ltd.) was used.

[0051] Oil temperature: 190° C.

[0052] Frying Conditions:

[0053] The refrigerated croquettes (7 croquettes; weight: about 75g/croquette) were fried over 5 minutes once every time shown in Table 2.After 2 minutes from the beginning of the frying, the croquettes in theoil composition were turned from side to side. The oil composition wasnewly supplied by an amount lost by the frying every hour (Examples 2 to4 and comparative Examples 1 to 3). This operation was repeated untilthe cumulative frying time amounted to 10 hours.

[0054] (Nitrogen Content in Oil Composition)

[0055] A part of the oil composition in the course of the frying wastaken out every 2 hours to measure a nitrogen content (%) by means of atotal nitrogen analyzer (TN-10 type, manufactured by Mitsubishi ChemicalIndustries, Ltd.).

[0056] (Coloring of Oil Composition)

[0057] A part of the oil composition in the course of the frying wastaken out every 2 hours to measure its redness (R) and yellowness (Y) inaccordance with the Lovibond method (Standard oils and fats analyzingtest method 2.2.1.1-1996; instrument used: Lovibond PFX880 Tintometer,using 1-inch glass cell), thereby finding a calculated value (10R+Y)thereof.

[0058] (Diglyceride Content in Oil Composition)

[0059] A part of the oil composition in the course of the frying wastaken out every 2 hours, and a silylating agent (product of KantoChemical Co., Inc.; 0.5 mL) was added to one drop of the oil compositionto conduct a reaction at 80° C. for 15 minutes, therebytrimethylsilylating the oil composition. After the reaction, thereaction mixture was washed with water and extracted with hexane, andthe extract was analyzed by gas chromatography to determine adiglyceride content (in accordance with the method described in JapanesePatent Application Laid-Open No. 10-176181).

[0060] In addition, odor in the vicinity of the fryer after 10 hoursfrom the beginning of the frying and cooked products fried at this timewere evaluated by 10 panelists in accordance with the followingevaluation standards.

[0061] (Odor Upon Frying)

[0062] A: Far excellent because no offensive odor such as an unpleasantburnt smell was emitted;

[0063] B: Excellent because offensive odor was scarcely emitted:

[0064] C: Some offensive odor was emitted;

[0065] D: Offensive odor was emitted.

[0066] (Degree of Coloring of Cooked Product)

[0067] A: Far excellent because the cooked products were colored only toan extent equivalent to those fried with Comparative Product 1;

[0068] B: Excellent because the cooked products were colored only to anextent almost equivalent to those fried with Comparative Product 1;

[0069] C: The cooked products were somewhat more colored compared withthose fried with Comparative Product 1;

[0070] D: The cooked products were strongly colored.

[0071] (Flavor of Cooked Product)

[0072] A: Far excellent because no unpleasant taste such as sourness orastringency taste was observed;

[0073] B: Excellent because an unpleasant taste was scarcely observed;

[0074] C: An unpleasant taste such as sourness or astringency taste wassomewhat observed;

[0075] D: Poor flavor because an unpleasant taste was observed. TABLE 2Time required to replace Frying interval of the whole oil Used oilcroquette (hr) Ex. 2 Invention Product 1 Fried once every 15 min. 14.9(fried 4 times in 1 hr.) Ex. 3 Invention Product 2 Fried once every 10min. 10.2 (fried 6 times in 1 hr.) Ex. 4 Invention Product 3 Fried onceevery 7.5 min.  7.7 (fried 8 times in 1 hr.) Comp. Comparative Product 1Fried once every 15 min. Not replaced Ex. 1 (fried 4 times in 1 hr.)Comp. Invention Product 2 Fried once every 30 min. 33.3 Ex. 2 (friedtwice in 1 hr.) Comp. Further adding rosemary Fried once every 30 min.33.3 Ex. 3 extract¹⁾ (2500 ppm) and (fried twice in 1 hr.) L-ascorbylpalmitate²⁾ (250 ppm) as antioxidants to Invention Product 2

[0076] TABLE 3 Properties of frying oil Diglyceride content in fryingoil (%) MG content in frying AV of oil frying Nitrogen content (%)Color(10 R + Y) after oil After After After 10 hr after 2 hr 4 hr 6 hr 8hr 10 hr 2 hr 4 hr 6 hr 8 hr 10 hr 2 hr 4 hr 6 hr 8 hr 10 hr (%) 10 hrEx. 2 0.01 0.03 0.04 0.05 0.06 43 58 79 93 115 21.5 20.8 20.5 19.9 19.50.5 2.1 Ex. 3 0.02 0.04 0.05 0.06 0.07 44 65 114 131 150 42.6 41.9 42.241.0 40.5 0.9 2.3 Ex. 4 0.02 0.04 0.07 0.11 0.15 45 68 158 215 250 84.384.2 84.0 83.4 83.2 1.9 2.4 Comp. 0.01 0.02 0.03 0.04 0.05 42 55 61 7591 0.8 1.3 1.3 1.5 2.4 — — Ex. 1 Comp. 0.02 0.05 0.09 0.18 0.31 45 74198 397 593 42.5 41.6 36.4 35.5 33.4 — — Ex. 2 Comp. 0.02 0.05 0.08 0.190.31 66 93 220 418 612 42.4 41.8 37.3 35.6 32.5 — — Ex. 3 After 10 hrfrom the beginning of frying Cooked Cooking product Odor Color FlavorEx. 2 A A A Ex. 3 A A A Ex. 4 B B B Comp. A A A Ex. 1 Comp. C B C Ex. 2Comp. C B C Ex. 3

[0077] All the diglyceride oils (Invention Products 1 to 3) underwent noincrease of the nitrogen content so far as the time required to replacethe whole oil was as described in Examples 2 to 4, and none of coloring,emission of offensive odor and lowering of the diglyceride content werefacilitated. However, the nitrogen content was increased, and coloring,emission of offensive odor and lowering of the diglyceride content werefacilitated when the replacement of the oil was insufficient even thoughthe same diglyceride oil (Invention Product 2) as in Example 3 was usedlike Comparative Example 2. As described above, the flavor and color ofthe fry (cooked products) were good according to the production methodof the present invention. In addition, the frying oils were hard to becolored, and emission of offensive odor and lowering of the diglyceridecontent were prevented even under severe conditions that heating wasperformed at a high temperature for a long period of time. Further, thenitrogen content in the frying oil was increased merely by sufficientlyadding the antioxidants to the oil used in Comparative Example 2 asdescribed in Comparative Example 3. Coloring, emission of offensive odorand lowering of the diglyceride content were unable to be preventedaccording to Comparative Examples.

EXAMPLES 5 AND 6 Comparative Example 4

[0078] (Repeated Test on Frying)

[0079] Refrigerated croquettes were repeatedly fried in the same manneras in Example 3 except that the oil composition (Invention Product 2)prepared in Example 1 was used, and a treatment with a nitrogenadsorbent, which will be described subsequently, was performed. As withExample 3, the nitrogen content in the oil composition in the course ofthe frying and the degree of coloring of the oil composition in thecourse of the frying and cooked products were evaluated. In addition,odor in the vicinity of the fryer after 10 hours from the beginning ofthe frying and the flavor of cooked products fried at this time wereevaluated. The results are shown in Table 4.

[0080] (Treating Conditions of Frying Oil)

[0081] Adsorbent: Activated carbon (Brocoal B, product of TaiheiChemical Industry Co., Ltd.).

[0082] Concentration of Adsorbent Used:

[0083] 0.3% by weight/weight of oil (Example 5);

[0084] 1% by weight/weight of oil (Example 6); and

[0085] No use of adsorbent (Comparative Example 4).

[0086] Treating Conditions of Frying Oil:

[0087] The temperature of the oil was cooled to 100° C. every 2 hoursunder the frying conditions in Example 3. Activated carbon was dispersedin the cooled oil, and the resultant dispersion was stirred for 10minutes as it is. The activated carbon was separated off through filterpaper to evaluate the filtered oil as to frying as it is. In this time,the oil of an amount lost by the frying of croquettes was not newlysupplied. This operation was repeated until the cumulative frying timeamounted to 10 hours. TABLE 4 Properties of frying oil After 10 hr fromthe Nitrogen content (%) Color (10 R + Y) beginning of frying AfterAfter After After After After After After After After Cooking Cookedproduct 2 hr 4 hr 6 hr 8 hr 10 hr 2 hr 4 hr 6 hr 8 hr 10 hr Odor ColorFlavor Ex. 5 0.01 0.03 0.04 0.05 0.06 43 60 80 91 110 A A A Ex. 6 0.010.02 0.03 0.04 0.05 40 54 58 72 89 A A A Comp. 0.03 0.05 0.11 0.22 0.3545 86 206 453 647 C C C Ex. 4

[0088] When the frying oil was treated with the nitrogen adsorbent likeExamples 5 and 6, the nitrogen content was not markedly increased evenif replacement of the oil was not conducted, and neither coloring noremission of offensive odor was facilitated. However, the nitrogencontent was increased, and coloring and emission of offensive odor werefacilitated when the treatment with the nitrogen adsorbent was notconducted even though the same diglyceride oil (Invention Product 2) wasused like Comparative Example 4. As described above, the flavor andcolor of the fry (cooked products) were good according to the productionmethod of the present invention. In addition, the frying oils were hardto be colored, and emission of offensive odor was prevented even undersevere conditions that heating was performed at a high temperature for along period of time.

EXAMPLES 7 AND 8 Comparative Example 5

[0089] (Repeated Test on Frying)

[0090] Frying was repeatedly conducted in the same manner as in Example4 except that the following materials were fried in place of therefrigerated croquettes. As with Example 4, the nitrogen content andcoloring degree of the oil composition in the process of frying andcooked products were evaluated. In addition, odor in the vicinity of thefryer after 10 hours from the beginning of the frying and the flavor ofcooked products fried at this time were evaluated. The results are shownin Table 5.

[0091] (Material to be Fried)

[0092] Refrigerated vegetable croquettes (Example 7): A product of GreenHouse K.K. No egg component was contained in a coating (weight ofcroquette: about 75 g/croquette, weight ratio of the coating: about 35%,nitrogen content in the coating: about 1.25%).

[0093] Refrigerated French potatoes (Example 8): Produced in USA. Nocoating was used.

[0094] Refrigerated croquette (Comparative Example 5): The samerefrigerated croquettes as used in Examples 2 to 4.

[0095] (Frying Conditions)

[0096] Frying was conducted under the same conditions as in Example 4 toevaluate the oil compositions as to frying. In this time, the oil of anamount lost by the frying was not newly supplied. This operation wasperformed for 10 hours at a pace of 8 times in an hour. TABLE 5Properties of frying oil After 10 hr from the Nitrogen content (%) Color(10 R + Y) beginning of frying After After After After After After AfterAfter After After Cooking Cooked product 2 hr 4 hr 6 hr 8 hr 10 hr 2 hr4 hr 6 hr 8 hr 10 hr Odor Color Flavor Ex. 7 0.03 0.04 0.07 0.13 0.18 4465 149 280 350 B B B Ex. 8 0.03 0.04 0.05 0.08 0.11 43 61 118 173 204 AA A Comp. 0.03 0.06 0.16 0.32 0.48 46 113 319 604 918 C C C Ex. 5

[0097] In each of Examples 7 and 8 of the present invention, thenitrogen content in the frying oil was not markedly increased, andneither coloring nor emission of offensive odor was facilitated.However, the nitrogen content in the frying oil was increased, andcoloring and emission of offensive odor were facilitated when thematerials high in nitrogen content were fried even though the samediglyceride oil (Invention Product 3) was used like Comparative Example5. As described above, the flavor and color of the fry (cooked products)were good according to the production method of the present invention.In addition, the frying oil was hard to be colored even under severeconditions that heating was performed at a high temperature for a longperiod of time.

EXAMPLE 9

[0098] (Repeated Test on Frying)

[0099] The oil composition (Invention Product 4) prepared in Example 1was used to repeatedly fry sliced potatoes in the same manner as inExample 4. As with Example 4, the nitrogen content and coloring degreeof the oil composition in the process of frying, cooked products, odorafter 10 hours from the beginning of the frying and the flavor of cookedproducts fried at this time were evaluated. Further, the cooked products(potato chips) were packaged with an aluminum foil laminate to evaluatethem as to flavor after storing for 1 month. The results are shown inTable 6.

[0100] (Material to be Fried)

[0101] Sliced potatoes: After potatoes (Irish cobbler) were each peeled,sliced to a thickness of 1.5 mm, and washed with water and hot water inaccordance a method known per se in the art, water on the surfaces waswiped off.

[0102] (Frying Conditions)

[0103] In an operation, slices (500 g) of potato were fried for 3minutes in the oil to obtain potato chips. This operation was performedfor 10 hours at a pace of 12 times in an hour. The oil composition wasnewly supplied by an amount lost by the frying every hour (the timerequired to replace the whole oil: 7.0 hours). Temperature: 180° C.

[0104] (Storing Conditions)

[0105] Temperature: 20° C., humidity: 65±5%; 1 month.

[0106] Incidentally, the potato chips after the storage were evaluatedby 10 panelists in accordance with the following evaluation standards.

[0107] (Flavor of Stored Product)

[0108] A: Far excellent because no unpleasant taste such as acidity orastringency taste was observed;

[0109] B: Excellent because an unpleasant taste was scarcely observed;

[0110] C: An unpleasant taste such as acidity or astringency taste wassomewhat observed;

[0111] D: Poor flavor because an unpleasant taste was observed. TABLE 6Properties of frying oil After 10 hr from the beginning Nitrogen content(%) Color (10 R + Y) of frying Flavor of After After After After AfterAfter After After After After Cooking Cooked product stored 2 hr 4 hr 6hr 8 hr 10 hr 2 hr 4 hr 6 hr 8 hr 10 hr Odor Color Flavor product Ex. 90.01 0.02 0.03 0.04 0.05 43 58 74 93 101 A A A A

[0112] As shown in Example 9, potato chips good in flavor and color wereable to be produced according to the present invention. Coloring of thefrying oil and emission of offensive odor were prevented.

EXAMPLE 10

[0113] The oil composition (Invention Product 3) prepared in Example 1was used to repeatedly fry refrigerated potato slices (Royal Chef'sSliced Potato, product of Foods Supply Co.; 1 kg) having a thickness of5 mm once every 5 minutes (12 times in an hour). The cooking wasconducted at 190° C. by means of an electric fryer (FX-65, manufacturedby Mach Kiki K.K.) by using the oil in an amount of 24 kg. The amount ofthe oil was measured every one hour to discard a part of the oil in sucha manner that the amount of the oil was reduced to 19.2 kg and newlysupply the oil composition (4.8 kg) (the time required to replace thewhole oil is adjusted to 5 hours by this process). This cooking wascontinued until the cumulative frying time amounted to 16 hours. Thetemperature of the oil after completion of the 16-hour cooking wascooled to 100° C., and activated carbon (Brocoal B, product of TaiheiChemical Industry Co., Ltd.) was dispersed in a proportion of 1% basedon the oil. After the resultant dispersion was stirred for 10 minutes asit is, the activated carbon was separated off through filter paper. Thenitrogen content and the degree of coloring were determined as to theoil before and after the treatment with the activated carbon.

[0114] The oil (4.8 kg) was newly supplied to the oil (19.2 kg) afterthe treatment to further conduct the cooking for 2 hours under theabove-described conditions that the time required to replace the wholeoil had been adjusted to 5 hours. The nitrogen content in the oilcomposition and the degree of coloring of the oil composition as well asthe flavor and the degree of coloring of cooked products, and odor inthe vicinity of the fryer upon cooking were evaluated after 1 hour(cumulative frying time: 17 hours) and 2 hours (cumulative frying time:18 hours). The results are shown in Table 7. TABLE 7 Oil post-treatedafter Cooking time after the post-treatment (cumulative frying time) 16hr from the After 1 hour (17 hours) After 2 hours (18 hours) beginningof frying Oil Oil Nitrogen Nitrogen Upon Cooked Nitrogen Upon Cookedcontent Color content Color cooking product content Color Odor cookingproduct (%) 10 R + Y Odor (%) 10 R + Y Odor Odor Color Flavor (%) 10 R +Y Odor Odor Color Flavor 0.001 87 A 0.001 86 A A A A 0.002 92 A A A A

[0115] As shown in Table 7, the color and flavor of the fry (cookedproducts) were able to be excellently kept. The nitrogen content in thefrying oil was markedly reduced, and coloring of the oil and emission ofoffensive odor were also prevented.

[0116] As described above, according to the present invention, fry goodin appearance and flavor can be produced repeatedly without causingcoloring of an oil and emission of offensive odor in fried-foodfactories, daily dish shops, eating houses, restaurants, etc. where fryis mass-produced over a long period of time using adiglyceride-containing oil composition having an effect to reduce theaccumulation of body fat to prevent obesity.

What is claimed is:
 1. A method for producing fried foods, whichcomprises cooking with an oil composition containing at least 15% byweight of diglycerides as a frying oil, wherein the content of nitrogenin at least 5 liters of the oil composition is kept to 0.2% by weight orlower.
 2. The method according to claim 1, wherein the method forkeeping the nitrogen content in the oil composition to 0.2% by weight orlower is such that the frying is conducted under frying conditions thatthe time required to replace the whole oil, which is defined by thefollowing equation (1), amounts to 2 to 25 hours: Time required toreplace the whole oil (unit: hour)=(Total amount of oil in afryer)/(Average amount of new oil supplied per hour)  (1)
 3. The methodaccording to claim 1, wherein the method for keeping the nitrogencontent in the oil composition to 0.2% by weight or lower is such thatthe frying oil is treated with a nitrogen adsorbent.
 4. The methodaccording to claim 1, wherein the method for keeping the nitrogencontent in the oil composition to 0.2% by weight or lower is such thatmaterials of fry, whose nitrogen content is 2% by weight or lower, areused.
 5. The method according to claim 1, wherein the method for keepingthe nitrogen content in the oil composition to 0.2% by weight or loweris such that migration of nitrogen from materials of fry, whose nitrogencontent exceeds 2% by weight, into the frying oil is prevented.
 6. Themethod according to claim 1, wherein the method for keeping the nitrogencontent in the oil composition to 0.2% by weight or lower is such that 2or more of the methods according to claims 2 to 5 are combined with eachother.
 7. The method according to claim 1, wherein the method forkeeping the nitrogen content in the oil composition to 0.2% by weight orlower is a combination of the methods according to claims 2, 3 and 4 ora combination of the methods according to claims 2, 3 and 5, and thenitrogen content in the oil composition is kept to 0.05% by weight orlower.
 8. The method according to any one of claims 1 to 7, wherein theoil composition containing at least 15% by weight of diglycerides as thefrying oil comprises 50 to 5,000 ppm of an antioxidant.
 9. The methodaccording to any one of claims 1 to 8, wherein the oil compositioncontaining at least 15% by weight of diglycerides as the frying oilcomprises 50 to 2,000 ppm of an organic carboxylic acid.
 10. Fried foodsproduced by the method according to any one of claims 1 to 9.